lu|na|cy

lu|na|cy «LOO nuh see», noun, plural -cies.

1. insanity, especially intermittent insanity, formerly supposed to be brought about by the changes of the moon: »

In one of these fits of lunacy or distraction…I fell down, and struck my face (Daniel Defoe).

2. Figurative. extreme folly: »

It is lunacy to cross the Atlantic in a rowboat.